Method of determining the movement of heat in a subterranean formation using bacteria analysis



United States Patent 3,489,217 METHOD OF DETERMINING THE MOVEMENT OFHEAT IN A SUBTERRANEAN FORMATION USING BACTERIA ANALYSIS Ralph E.Gilchrist, Houston, Tex., assignor to Tenneco Oil Company, Houston,Tex., a corporation of Delaware N0 Drawing. Filed Oct. 29, 1968, Ser.No. 771,645 Int. Cl. E21b 43/24, 47/10 US. Cl. 166-246 7 Claims ABSTRACTOF THE DISCLOSURE A method of determining the movement of heat in asubterranean hydrocarbon bearing formation, such as during a thermalrecovery process. It includes the steps of instituting a lateral heatmovement in the formation. This heat movement generally causes thepercolation upward of hydrocarbon gases, such as methane. Thereafter,samples of soil from a plurality of spaced apart points on theoverburden are collected and analyzed to determine the relative bacteriacount of hydrocarbon gas feeding bacteria as indications of the extentof movement of the heat front.

This invention relates to a method of detecting the movement of heat inthe subterranean hydrocarbon bearing formation, as for example during athermal recovery process. It contemplates the use of bacteria analysisto detect the presence of a hydrocarbon gas in the overburden, whichhydrocarbon gas is found to exist in greater quantities in theoverburden where the heat has progressed.

The use of heat or a heat movement, such as the injection of steam, oran in-situ combustion, as a recovery agent in oil production providesthe opportunity to produce heavy crudes, heretofore consideredunrecoverable. In many instances, it is difficult to determine the arealinvasion of the heat movement, particularly if it does not manifestitself in some of the producing wells of a pattern.

Heretofore, other methods have been developed for determining this arealinvasion and such methods include the drilling of observation wellsbetween the injection and production bore holes, and the use of variousseismic techniques.

Still another method is taught in copending application Ser. No. 647,710filed June 21, 1967 by the applicant. The method of that applicationutilizes thermocouples.

None of these processes are fully satisfactory in all situations. Forexample, the drilling of observation holes is quite expensive. Withrespect to the use of thermocouples, certain overburdens may provideinsulation means which prevents uniform transmission of heat through theoverburden. Further, seismic data is often very difficult to interpret.

It is therefore an object of this invention to provide an improvedmethod for detecting the movement of heat in a subterranean hydrocarbonbearing formation, as for example during a thermal recovery process, andwhich is not subject to some of the limitations of the prior artmethods.

Briefly stated, this invention is for a method of determining the extentof areal invasion of heat in a subterranean hydrocarbon bearingformation, as for example during a thermal recovery operation. Themethod comprises instituting or initiating a lateral heat movement inthe hydrocarbon bearing formation. It is to be understood that the heatmovement can be in the form of steam injection from one injection wellto another production well, or it may be in a huff and putt cyclical3,489,217 Patented Jan. 13, 1970 "ice injection system. Further, it maybe an in-situ combustion type wherein the heat front is initiated in thehydrocarbon bearing formation. In any event, once the heat movement iscommenced, samples of soil from a plurality of spaced apart points onthe overburden are collected. These samples are then tested to determinethe relative amount of hydrocarbon gas feeding bacteria in the samplesas indications of the extent of areal movement of the heat front. It isto be understood that as the heat front advances in a formation,hydrocarbon gases, such as methane, are found to percolate upwardthrough the overburden therebystimulating the growth of bacteria feedingon such hydrocarbon gases.

In certain embodiments of the invention, the aforesaid testing iscarried out by adding a culture medium to the soil sample, after whichthe samples are contacted with an atmosphere containing a substantialamount of hydrocarbon gas, such as methane. Thereafter, the amount ofhydrocarbon gas consumed by the bacteria in the sample is then measuredto determine the relative quantity or bacteria count for the samples, asa measure of the extent of areal movement of the heat front. The testingcan be repeated at intervals of one or more days, with those samplesshowing the earliest and greatest amount of loss of the hydrocarbon gasfrom the sample indicating the sample having the highest bacteria count.

The method of the present invention is particularly useful in fieldssuch as the Chetopa field of Labette County, Kansas, where thehydrocarbon bearing formation, was at a relatively shallow depth on theorder of 82-100 feet.

In carrying out the invention, stream is injected through an injectionbore hole in conventional manner and caused to move laterally in thehydrocarbon bearing formation, which will sometimes hereinafter bereferred to as instituting a lateral heat movement therein. It is to beunderstood that an in-situ combustion following conventional methodscould also be used as a means for instituting a lateral heat movement.

As the heat movement progresses, it has been found that there is atendency for hydrocarbon gases, such as methane, to percolate upwardlythrough the overburden to the surface thereabove. This added presence ofthe hydrocarbon gas stimulates the growth of hydrocarbon gas feedingtype bacteria in the soil above the heated hydrocarbon formation.

Soil samples are taken from a few inches below the soil surface atspaced apart intervals extending away from the injection bore hole andin the general direction or directions of the anticipated heat movement.These soil samples are then analyzed for the relative presence ofbacteria of the hydrocarbon gas feeding type according to known methods.For example, the article entitled Comparison of GeomicrobiologicalProspecting Methods Used by Various Investigators by D. O. Hitzman andcarried in the book entitled Developments in Industrial Microbiology,volume 2 published by Plenum Press Incorporated, 227 W. 17th St., NewYork 11, N.Y., and the articles referred to therein discuss varioustesting and analyzing procedures to test for the relative presence ofhydrocarbon consuming bacteria in soil samples.

The method which the applicant used in testing for the presence ofhydrocarbon gas feeding bacteria was to place the soil samples instoppered serum bottles with 15 ml. of a culture medium per 7.5 grams ofsoil. Thereafter the serum bottles were connected to a manometer and thebottles flushed with a gas comprising approximately A methane and /3air. It is to be understood that this ratio could be on the order of 50%methane and 50% air. The manometer was used to measure gas uptake by thebacteria present in the bottle.

The particular manometer used was the U-tube type and the pressurechange was read and multiplied by two to give the reading of thedecrease in pressure caused by he consumption of the hydrocarbon gas inthe atmosghere contacting the sample.

The bottles with the fastest and most gas uptake would 3f course reflectthose containing the most hydrocarbon gas consuming bacteria. Thesereadings can be taken at intervals of one or more days over a period ofseveral lays, such as a month.

In some instances it may be desirable to use a control sample with eachtest sample, where in the control sample is flushed with an atmospherecontaining approximately V3 nitrogen and /a air or some othernon-hydrocarbon type gas. Thus, if the reduction in pressure on themanom- :ter were caused by some other factor than the bacteria oeingtested for, it would become apparent.

It was found that those soil samples overlying the hyirocarbon formationthrough which the heat had'advanced generally had a reading indicating ahigher hydrocarbon gas feeding bacteria count, than those samples takenfrom areas overlying the formation through which the heat front had notadvanced.

It will thus be apparent that this invention provides an improved meansfor determining the areal invasion of heat in a reservoir. The presentinvention is simple and inexpensive as compared with prior art methodsrequiring observation wells that are costly to drill and/or seismicrecords which are diflicult to interpret.

During recovery processes utilizing steam drive or cyclical injection, agreat amount of heat is required to raise the temperature of the portionof the reservoir containing the hydrocarbon material. In many instances,the reservoir is overheated because it is difficult to predict the sizeof the steam stimulation treatment. By the use of this invention, themovement of the heat can be detected to determine the areal invasionthereby eliminating possible overheating of the formation.

It is to be understood that the foregoing description is generallyillustrative of the invention, which will admit of the many differentembodiments.

What is claimed is:

1. In a method of detecting the movement of heat in a subterraneanhydrocarbon bearing formation, the combination of steps comprising:

instituting a lateral heat movement in said hydrocar- 2. The method fordetermining the extent of areal invasion of heat in a subterraneanhydrocarbon bearing formation during a thermal recovery operation, saidmethod comprising the steps of:

initiating a lateral heat movement in said hydrocarbon bearingformation;

collecting samples of soil from a plurality of spaced apart points onthe overburden above said formation;

and testing said samples to determine the relative amount of hydrocarbongas feeding bacteria in Said samples as indications of the extent ofareal movement of said heat.

3. The invention as claimed in claim 2 wherein:

said bacteria is of the methane feeding type.

4. In a method detecting the movement of heat in a subterraneanhydrocarbon bearing formation during a thermal recovery operation, thecombination of steps comprising:

initiating -a lateral heat movement in said formation;

collecting samples of soil from a plurality of spaced apart points onthe overburden above said formation;

adding a culture medium to said samples;

subjecting s-aid samples to an atmosphere containing a substantialamount of a hydrocarbon gas;

and measuring the amount of said hydrocarbon gas consumed by bacteriacontained in each of said samples as indications of the extent of arealmovement of said heat.

5. The invention as claimed in claim 4 wherein:

said hydrocarbon gas includes methane and said bacteria is of themethane consuming type.

6. The invention as claimed in claim 4 wherein:

said measuring step is performed by connecting a manometer to each ofsaid samples, and the change in pressure caused by the consumption ofhydrocarbon gas in each of said samples is read therefrom.

7. The invention as claimed in claim 4 wherein:

said measuring step for each of said samples is at least one daysubsequent to said first measuring step.

References Cited UNITED STATES PATENTS 5/1943 Hodell et a1. 166-2525/1962 Parker 166251 X U.S. Cl. X.R. l66251, 252

